This invention relates to the art of transformers and, more particularly, to improvements in transformers for supplying energy to an inductor for inductively heating workpieces such as crankshafts.
Transformers particularly suited for use in connection with the inductive heating of workpieces such as crankshafts are well known and have an output side directly connected to the inductor for inductively heating a bearing surface of a crankshaft. Transformers of the foregoing character are shown, for example, in U.S. Pat. Nos. 3,300,614 to Sorensen; 3,503,026 to Geisel et al; 3,728,655 to Reinke and 3,936,783 to Wagemer, the disclosures of which are hereby incorporated herein by reference for background purposes. The output side of the secondary of such a transformer is directly connected to the inductor, such as through the use of terminal members, and the inductor is associated with the crankshaft in a manner whereby rotation of the crankshaft during induction heating is translated into oscillating movement of the transformer unit. The primary and secondary of the transformer as well as the inductor can be of tubular construction to facilitate the flow of coolant therethrough, and the primary and secondary are associated with a core of suitable ferromagnetic material. Connections are provided for communicating the primary and secondary as well as the inductor with a source of coolant. The coolant connections for the secondary, and often the inductor, are at the output end of the secondary where the secondary is connected to terminal blocks for connection with the inductor. The primary, at the opposite end of the transformer, is often provided with terminals providing taps to enable changing the primary to secondary ratio of the transformer. As is further known from such art, the primary and secondary can be interleaved, and the windings arranged for the transformer to have a flat-pancake profile. It is further known in the industry to provide for the secondary to comprise a plurality of individual loops interposed between adjacent convolutions of the primary and having opposite ends connected to a corresponding terminal member, such loops being tubular and connected with the terminal members to accommodate coolant flow through the secondary. In view of the nature of the use of the transformer in connection with inductively heating a crankshaft, and the disposition of the transformer relative to the crankshaft, it is of course desirable to provide for all the foregoing component parts thereof to have as thin a dimension as possible relative to a plane between the opposite ends of the transformer and transverse to the crankshaft axis.
In pancake-type transformers of the foregoing character heretofore provided, the terminal members by which the secondary is connected to the inductor and the portions of the primary and secondary at the end of the transformer at which the secondary is connected to the terminal members are exposed outwardly of the core which encloses the primary and secondary. The terminal blocks may, for example, be five to six inches long measured from the outermost portion of the primary and secondary and the point of connection between the terminal blocks and the inductor, and the terminal blocks together may measure about four inches wide in the plane of the transformer. This provides an area of considerable size and in which there is a considerable power loss during an induction heating operation. Another problem which primarily affects the economy of construction of such transformers is the plumbing configuration or configurations required to connect the transformer secondary and the inductor to a coolant source or sources. More particularly in this respect, either the coolant source connections have to be provided on laterally opposite sides of the transformer or, as shown in the Wagemer patent referred to above, provided on one side through the use of structurally complex conductor configurations. Yet another problem encountered with prior art pancake-type transformers is that the terminals providing taps for adjusting the primary to secondary ratio of the transformer have to be dimensionally accurate and of different contours, both of which add to the cost of the construction of the transformer. More importantly, in response to oscillation of the transformer during the induction heating of a rotating crankshaft the tap contacts are stressed by the flexible cables which are attached thereto and extend to a fixed location spaced from the transformer and at which tap changing is achieved. Such stressing of the tap contacts leads to fatigue thereof and/or the brazed connection thereof to the transformer winding, both of which result in undesirable down time for maintenance or replacement.